The present invention relates to the field of conversion of carbometallic oils to products such as gasoline and other liquid hydrocarbon fuels usually with less coke formation produced, increased yield and selectivity, with lower gas formers, e.g. diolefins, produced, utilizing the hydrogenation potential of the accumulated metals.
An oil such as a crude oil, crude oil fraction or other oil that is particularly abundant in nickel, vanadium, and/or other heavy metals which exhibit similar behavior while also containing relatively large quantities of coke precursors, is referred to herein as a carbometallic oil, and represents a particular challenge to the petroleum refiner in his attempt to convert it into gasoline and other liquid hydrocarbon fuels.
In general, gasoline and other liquid hydrocarbon fuels boil in the range of about 100.degree. F. (38.degree. C.) to about 650.degree. F. (343.degree. C.), however, the crude oil from which these fuels are made is a diverse mixture of hydrocarbons and other compounds which vary widely in molecular weight and therefore boil over a wider range. For example, crude oils are known in which 30% to 60% or more of the total volume is composed of compounds boiling at temperatures above 650.degree. F. (343.degree. C.). Among these crudes are crudes in which about 10% to about 30% or more of the total volume consists of compounds which are so heavy in molecular weight that they boil above 1025.degree. F. (552.degree. C.), or at least will not boil below 1025.degree. F. (552.degree. C.) at atmospheric pressure.
Because these relatively abundant high boiling components of crude oil are unsuitable for inclusion in gasoline and other liquid hydrocarbon fuels, the Fluid Catalytic Cracking (FCC) process was developed for cracking or breaking the molecules of high molecular weight, high boiling compounds into smaller molecules which boil over an appropriate boiling range. Although the FCC process has reached a highly advanced state, and many modified forms and variations have been developed, their unifying factor is that a vaporized hydrocarbon feedstock which contains high molecular weight, high boiling components is caused to crack at an elevated temperature in contact with a cracking catalyst that is suspended in the feedstock vapors. Upon attainment of the desired molecular weight and boiling point reduction, the catalyst is separated from the desired products.
The present invention is concerned with using hydrocarbon feedstocks which have higher Ramsbottom carbon values than are indicative of acceptable FCC feedstock and thus exhibit a substantially greater potential for coke formation than does the usual FCC feedstock. In conventional FCC practice, Ramsbottom carbon values on the order of about 0.1 to about 1.0 are regarded as indicative of acceptable feed. Conventional FCC practice has employed as feedstock that fraction of crude oil which boil at about 650.degree. F. (343.degree. C.) to about 1000.degree. F. (538.degree. C.), and is relatively free of coke precursors and heavy metal contaminants. Such feedstock, known as "vacuum gas oil" (VGO), is generally prepared from crude oil by distilling off the fractions boiling below about 650.degree. F. (343.degree. C.) at atmospheric pressure and then separating, by further vacuum distillation from the heavier fractions, a cut boiling between about 650.degree. F. (343.degree. C.) and about 900.degree. F. (482.degree. C.) to 1025.degree. F. (552.degree. C.).
Since the various heavy metals in carbometallic oil are not of equal catalyst poisoning activity, it is convenient to express the poisoning activity of an oil containing a given poisoning metal or metals in terms of the amount of a single metal which is estimated to have equivalent poisoning activity. Thus, the heavy metals content of an oil can be expressed by the following formula (patterned after that of W. L. Nelson in Oil and Gas Journal, page 143, Oct. 23, 1961) in which the content of each metal present is expressed in parts per million of such metal, as metal, on a weight basis, based on the weight of feed: EQU Nickel Equivalents=Ni+(V/4.8)+(FE/7.1)+(Cu/1.23)
The above formula can also be employed as a measure of the accumulation of heavy metals on the cracking catalyst, except that the quantity of metal employed in the formula is based on the weight of catalyst (moisture free basis) instead of the weight of feed.
The present invention is concerned with using hydrogen gas in the processing of feedstocks containing heavy metals substantially in excess of that useful in conventional FCC processing, and which therefore have a significantly greater potential for accumulating on and poisoning the catalyst.